Add link to Keycloak account console to account dropdown

[lukasrad02]

As we now support first name changes trough our Keycloak account console, I would propose to add a link to the console to the account menu in the header. This would

• increase visibility of the account console and especially the name change feature
• be somewhat consistent with how name changes on EvaP work (name changes are handles directly by EvaP, but the link to the form in is the account menu in the header too)
• be consistent with general UI design and user's assumptions